Solid addition polymer-based microspheres have found many uses. In coatings, such microspheres have been used as additives for rheology control and as vehicle components of dispersion coatings. Aqueous dispersion coatings use dispersed meth(acrylic)-based vehicle components prepared straightforwardly by emulsion polymerization. Emulsion polymerization, however, typically uses emulsifiers that may make a coating more water-sensitive or that may contribute to poor coating durability.
The additives for rheology control have been prepared by less straightforward means. [The term (meth)acrylic will be used to indicate acrylic and/or methacrylic; the term (meth)acrylate will be used to indicate acrylate and/or methacrylate.] In a first method, the rheology control additives have been prepared by emulsion polymerization and then transferred into a nonaqueous dispersion medium. In a second method, the rheology control additives have been prepared by a nonaqueous dispersion reaction in weak solvents and then transferred from the weak solvents into a different organic medium suitable for a coating composition. Both methods are complex and generate undesirable waste from the media replacements.
Solid addition polymer-based particulates have also been used in powder coating compositions. Powder coating compositions are prepared by melt mixing solid polymers, pigments, and other ingredients in an extruder and grinding the extrudate, and classifying to powder to obtain the desired average particle size and particle size distribution.
In WO 98/45054, Butler et al. describe dispensing a continuous flow of a first fluid into a second fluid and onto a substrate. The chemical composition of the first fluid is altered before it contacts the substrate. The continuous fluid flows are produced, e.g., by curtain coating, slide coating, extrusion die coating, and roll coating. The WO 98/45054 document in particular describes silicone pre-polymers dispensed alone or with a carrier fluid. Preferred fluids are silicone-urea release formulations, silicone or fluorosilicone polymers, and other adhesive polymers. The fluid may contain a silyl hydride crosslinker, thermal and ultraviolet initiated platinum catalysts, chemical additives and modifiers, and particulate solids. The second fluid is chosen so that it does not interrupt the continuous flow of the first fluid. A condition, for example actinic radiation, is imposed on the first fluid. The first fluid is applied to a substrate, either as a “landing spot” from which the first fluid can be released or a coating. The process is described as useful for partially or fully curing a fluid curtain of a low viscosity formulation to increase its viscosity before deposition onto a substrate, or for polymerization of pre-polymers before they contact a heat- or light-sensitive substrate or multi-layer coating. The process could also be used to generate patterned or porous membranes or films in a fluid carrier coating method.
While the WO 98/45054 produces coatings directly on a substrate or continuous films that can be released from a substrate, a continuous film or coating layer would not be useful for improving the long-standing problems described earlier with preparing rheology control additives and powder coating compositions. Factories that already have installed coatings application equipment for liquid coating or powder coating compositions wish to continue applying such coating compositions. Accordingly, it would be beneficial to have an improved process for manufacturing liquid or powder coating compositions.